Window and method of manufacturing the same

ABSTRACT

A window includes a base region and a compressive stress region disposed on the base region. The compressive stress region includes Li + , Na + , and K +  ions. The compressive stress region includes a first compressive stress portion in which a concentration of the K +  ions decreases, a concentration of Na +  ions increases, and a concentration of the Li +  ions increases, from a surface of the window toward the base region. A second compressive stress portion is adjacent to the first compressive stress portion. In the second compressive stress portion, the concentration of the Na +  ion decreases and the concentration of the Li +  ion increases, from the first compressive stress portion toward the base region. The window thereby has a high surface compressive stress value and impact resistance.

CROSS-REFERENCE TO RELATED APPLICATION

This U.S. non-provisional patent application claims priority under 35U.S.C. § 119 of Korean Patent Application No. 10-2019-0063793, filed onMay 30, 2019, the entire contents of which are hereby incorporated byreference.

TECHNICAL FIELD

The present disclosure herein relates to a window and a method ofmanufacturing the same, and more particularly, to a window used as acover glass of an electronic device and a method of manufacturing thesame.

DISCUSSION OF THE RELATED ART

An electronic device may include a window, a housing, and variouselectronic elements disposed therein. One such electronic element may bea display device for displaying an image. The various electronicelements may also include a touch sensor as well as one or more elementsfor generating and/or detecting light and/or sound.

The window protects the electronic elements and provides a user with anactive region in which a display may be seen and in which the user mayregister touch inputs. Accordingly, the user provides an input to theelectronic elements or receives information generated by the electronicelements, through the window. Further, the electronic elements may bestably protected from external impact due to the window.

In recent years, the trend of slimming electronic devices demands alighter and thinner window, and to compensate for structural weaknessresulting therefrom, a method of toughening a window has been studied bywhich excellent strength and surface durability are provided.

SUMMARY

The present disclosure provides a window having increased compressivestress and impact strength of a surface.

In addition, the present disclosure provides a method of manufacturing awindow, which includes a toughening process for increasing compressivestress and impact strength of a surface.

An embodiment of the present inventive concept provides a windowincluding a base region and a compressive stress region which isdisposed on the base region. The compressive stress region includes Li⁺,Na⁺, and K⁺ ions, and further includes a first compressive stressportion in which, from a surface of the window toward the base region,the concentration of the K⁺ ion decreases, and the concentration of theNa⁺ ion and the concentration of the Li⁺ ion increase. A secondcompressive stress portion is adjacent to the first compressive stressportion. In the second compressive stress portion, from the firstcompressive stress portion toward the base region, the concentration ofthe Na⁺ ion decreases and the concentration of the Li⁺ ion increases.

In an embodiment of the present inventive concept, the first compressivestress portion may have a first compressive stress pattern in which acompressive stress value decreases with a first slope from the surfacetoward the base region. The second compressive stress portion may have asecond compressive stress pattern in which the compressive stress valuedecreases with a second slope different from the first slope, from thefirst compressive stress portion toward the base region. Each of thefirst slope and the second slope may represent a decrease in thecompressive stress value as a depth inside the window increases in adirection from the surface toward the base region.

In an embodiment of the present inventive concept, the first slope maybe greater than the second slope.

In an embodiment of the present inventive concept, a density at thefirst compressive stress portion may be greater than a density at thesecond compressive stress portion.

In an embodiment of the present inventive concept, the secondcompressive stress portion might not comprise the K⁺ ion.

In an embodiment of the present inventive concept, the thickness of thecompressive stress region may be within a range from about 130 μm toabout 150 μm.

In an embodiment of the present inventive concept, the thickness of thefirst compressive stress portion may be within a range from about 5 μmto about 15 μm

In an embodiment of the present inventive concept, a compressive stressvalue at the surface may be about 650 MPa or larger.

In an embodiment of the present inventive concept, the base region mayinclude SiO₂ of from about 50 wt % to about 80 wt %, Al₂O₃ of from about10 wt % to about 30 wt %, and Li₂O₃ of from about 3 wt % to about 20 wt%.

In an embodiment of the present inventive concept, the window mayinclude a flat portion and at least one bent portion adjacent to theflat portion.

In an embodiment of the present inventive concept, a window includes acompressive stress region at a surface thereof. The compressive stressregion includes a first compressive stress portion in which, from thesurface toward a center of the window, the concentration of K⁺ iondecreases, and the concentration of Na⁺ ion and the concentration of Li⁺ion increase. A second compressive stress portion is adjacent to thefirst compressive stress portion. In the second compressive stressportion, from the first compressive stress portion toward the center,the concentration of the Na⁺ ion decreases and the concentration of theLi⁺ ion increases.

In an embodiment of the present inventive concept, the first compressivestress portion may have a first compressive stress pattern in which acompressive stress value decreases with a first slope from the surfacetoward the center. The second compressive stress portion may have asecond compressive stress pattern in which the compressive stress valuedecreases with a second slope greater than the first slope, from thefirst compressive stress portion toward the center. Each of the firstslope and the second slope may represent a decrease in the compressivestress value as a depth inside the window increases from the surfacetoward the center.

In an embodiment of the present inventive concept, a method ofmanufacturing a window includes providing a base glass and tougheningthe base glass. The toughening of the base glass includes performing afirst toughening of the base glass in a first toughening molten salt,performing a second toughening of the base glass in a second tougheningmolten salt, and performing a third toughening of the base glass in athird toughening molten salt. The first to third toughening molten saltseach include KNO₃ and NaNO₃, and the weight percentage of the KNO₃ inthe second toughening molten salt is greater than the weight percentagesof the KNO₃ in the first toughening molten salt and the third tougheningmolten salt.

In an embodiment of the present inventive concept, the weight ratio ofthe KNO₃ and the NaNO₃ in the second toughening molten salt may bewithin a range from about 91:9 to about 90:10.

In an embodiment of the present inventive concept, each of the weightratios of the KNO₃ and the NaNO₃ in the first toughening molten salt andthe third toughening molten salt may be within a range from about 40:60to about 60:40.

In an embodiment of the present inventive concept, the base glass mayinclude SiO₂, Al₂O₃, and Li₂O₃.

In an embodiment of the present inventive concept, the base glass mayinclude SiO₂ of from about 50 wt % to about 80 wt %, Al₂O₃ of from about10 wt % to about 30 wt %, and Li₂O₃ of from about 3 wt % to about 20 wt%.

In an embodiment of the present inventive concept, the base glass mayfurther include Na₂O.

In an embodiment of the present inventive concept, the toughening of thebase glass may be performed at a temperature of from about 350° C. toabout 450° C.

In an embodiment, the first toughening molten salt may further includeH₂O₃Si or zeolite.

BRIEF DESCRIPTION OF THE FIGURES

A more complete appreciation of the present disclosure and many of theattendant aspects thereof will be readily obtained as the same becomesbetter understood by reference to the following detailed descriptionwhen considered in connection with the accompanying drawings, wherein:

FIG. 1 is a perspective view illustrating an electronic device accordingto an embodiment of the present inventive concept;

FIG. 2 is an exploded perspective view illustrating the electronicdevice illustrated in FIG. 1 ;

FIG. 3 is a perspective view illustrating a window according to anembodiment of the present inventive concept;

FIG. 4 is a cross-sectional view illustrating a window of an embodimentof the present inventive concept;

FIG. 5A is a graph schematically illustrating an ion concentrationdistribution in the window of an embodiment of the present inventiveconcept;

FIG. 5B is a graph schematically illustrating a compressive stressprofile in the window of an embodiment of the present inventive concept;

FIGS. 6A to 6C are each a graph schematically illustrating a compressivestress distribution in the window of an embodiment of the presentinventive concept;

FIG. 7 is a flowchart illustrating a method of manufacturing a windowaccording to an embodiment of the present inventive concept;

FIG. 8 is a flowchart illustrating a toughening process in a method ofmanufacturing a window according to an embodiment of the presentinventive concept; and

FIG. 9 is a schematic diagram illustrating a toughening process in amethod of manufacturing a window according to an embodiment of thepresent inventive concept.

DETAILED DESCRIPTION

In describing embodiments of the present disclosure illustrated in thedrawings, specific terminology is employed for sake of clarity. However,the present disclosure is not intended to be limited to the specificterminology so selected, and it is to be understood that each specificelement includes all technical equivalents which operate in a similarmanner.

It will be understood that when an element or layer is referred to asbeing “on”, “connected to” or “coupled to” another element or layer, itcan be directly on, connected or coupled to the other element or layer,or intervening elements or layers may be present.

Like reference numerals may refer to like elements throughout thisspecification and figures. In the figures, the thicknesses, ratios anddimensions of elements may be exaggerated for effective description ofthe technical contents.

It will be understood that, although the terms first, second, etc. maybe used herein to describe various elements, components, regions, layersand/or sections, these elements, components, regions, layers and/orsections should not be limited by these terms. These terms are only usedto distinguish one element, component, region, layer or section fromanother element, component, region, layer or section. Thus, a firstelement, component, region, layer or section discussed below could betermed a second element, component, region, layer or section withoutdeparting from the teachings of the present invention. As used herein,the singular forms, “a”, “an” and “the” are intended to include theplural forms as well, unless the context clearly indicates otherwise.

Spatially relative terms, such as “beneath”, “below”, “lower”, “above”,and “upper”, may be used herein for ease of description to describe oneelement or feature's relationship to another element(s) or feature(s) asillustrated in the figures. It will be understood that the spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures.

Hereinafter, a window, according to an embodiment of the presentinventive concept, and a method of manufacturing a window, according toan embodiment of the present inventive concept, will be described hereinwith reference to the accompanying drawings.

FIG. 1 is a perspective view illustrating an electronic device inaccordance with an embodiment of the present inventive concept. In FIG.1 , an electronic device including a window is shown. FIG. 2 is anexploded perspective view of the electronic device illustrated in FIG. 1. FIG. 3 is a perspective view of a window according to an embodiment ofthe present inventive concept. FIG. 4 is a cross-sectional view of thewindow. FIG. 5A shows an ion concentration distribution in the window,and FIG. 5B shows a compressive stress profile in the window.

The electronic device EA may be embodied as a smart phone, a smartwatch, a personal computer, a tablet computer, alaptop/notebook/Ultrabook computer, a desktop computer monitor, atelevision set or the like. The electronic device EA may include variousembodiments such as a display device, elements for generatingsound/light, elements for sensing sound/light and one or more otherelectronic elements.

The electronic device EA may display an image IM in a third directionDR3 on a display surface IS that is parallel to a plane defined by afirst direction DR1 and a second direction DR2. The display surface ISon which the image IM is displayed may correspond to a front surface ofthe electronic device EA and a front surface FS of a window CW. Further,the electronic device EA may have a three-dimensional shape having apredetermined thickness in the third direction DR3 that is perpendicularto the plane defined by the first direction DR1 and the second directionDR2.

The display surface IS in the electronic device EA illustrated in FIG. 1may include a display region DA and a non-display region NDA adjacent tothe display region DA. The non-display region NDA may at least partiallysurround the display region DA. The non-display region NDA isillustrated as fully surrounding the display region DA, but the presentinventive concept is not limited thereto. The display region DA is aregion in which the image IM is provided and thus may correspond to anactive region AA of a display panel DP. The image IM may be a stillimage and/or a dynamic image. A clock window is illustrated in FIG. 1 asan example of the image IM.

In this embodiment, the terms front/top surface and rear/bottom surfaceare defined in relation to a direction in which the image IM isdisplayed. The front surface and the rear surface may be opposed to eachother in relation to the third direction DR3, and a normal direction ofeach of the front surface and the rear surface may be parallel to thethird direction DR3. The first to third directions DR1 to DR3 are arelative concept and may be converted into different directions.

The electronic device EA includes the window CW, the display panel DP,and a housing HAU. In the electronic device EA, as shown in FIGS. 1 and2 , the window CW and the housing HAU may be combined to constitute theexterior of the electronic device EA.

The front surface FS of the window CW defines the front surface of theelectronic device EA, as described in detail. The front surface FS ofthe window CW may include a transmissive region TA in which light maypass and a bezel region BZA in which light may be at least partiallyblocked.

The transmissive region TA may be an optically transparent region. Forexample, the transmissive region TA may be a region having a visiblelight transmittance of about 90% or greater.

The bezel region BZA may have a lower light transmittance than thetransmissive region TA. The bezel region BZA may define the shape of thetransmissive region TA. The bezel region BZA may be adjacent to and mayat least partially surround the transmissive region TA.

The bezel region BZA may be of a particular color such as black. Thebezel region BZA may cover a peripheral region NAA of the display panelDP to block the peripheral region NAA from being viewed from theoutside. This is illustrated in the figures by way of example, however,the bezel region BZA may be omitted from the window CW according to anembodiment of the present inventive concept.

The window CW may include a glass substrate. For example, the window CWmay be a toughened glass substrate that has undergone a tougheningprocess. The window CW may provide the transmissive region TA byutilizing the light transmittance of the glass and may stably protectthe display panel DP from external impact by virtue of including atoughened surface.

The window CW may be manufactured in accordance with the methods setforth herein. A method of manufacturing a window in accordance with anembodiment of the present inventive concept may include multiple-stagetoughening for toughening a base glass, and a toughening molten salt maybe provided in each stage of the multiple-stage toughening. A detaileddescription of the method of manufacturing a window is provided below.

The display panel DP may be activated according to an electrical signal.In this embodiment, the display panel DP is activated to display theimage IM on the display surface IS of the electronic device EA. Theimage IM may be viewed by a user through the transmissive region TA, andthe user may receive information from the image IM. However, this isillustrated by way of example, and the display panel DP may be activatedto sense an external input applied to a front surface thereof. Theexternal input may include a touch of a user, contact or proximity of aninanimate object, pressure, light, or heat, and is not limited to anyone particular embodiment.

The display panel DP may include the active region AA and the peripheralregion NAA. The active region AA may be a region in which the image IMis provided. The transmissive region TA may overlap at least a portionof the active region AA.

The peripheral region NAA may be a region covered by the bezel regionBZA. The peripheral region NAA may be adjacent to the active region AA.The peripheral region NAA may at least partially surround the activeregion AA. A drive circuit, drive wires or the like for driving theactive region AA may be disposed in the peripheral region NAA.

The display panel DP may include a plurality of pixels PX. Each of theplurality of pixels PX displays a point of light in response to anelectrical signal. The light displayed by the pixels PX implements theimage IM. The pixel PX may include a display element. For example, thedisplay element may be an organic light emitting element, a quantum dotlight emitting element, a liquid crystal display element, anelectrophoretic element, an electrowetting element, or the like.

The housing HAU may be disposed below the display panel DP. The housingHAU may include a relatively stiff/rigid material. For example, thehousing HAU may include a plurality of frames and/or plates constitutedof glass, plastic, or metal such as stainless steel or aluminum. Thehousing HAU defines an accommodation space for accommodating the displaypanel DP and other electronic elements. The display panel DP may beprotected from external impact by the housing HAU.

FIG. 3 is a perspective view illustrating a window CW-a according to anembodiment of the present inventive concept. This window CW-a isillustrated in FIG. 3 , and may include one or more bent portions BAthat are each bent around a bending axis BX. In an embodiment of thepresent inventive concept, the window CW-a may include a flat portion FAand the bent portions BA. The flat portion FA may be disposed betweentwo bent portions BA, as shown, however, in some embodiments of thepresent inventive concept, there might be only one bent portion BA orthere may be no flat portion as the entire front surface FS may be bent.

In an embodiment of the present inventive concept, the bending axis BXmay extend in the second direction DR2 and may be provided on a rearsurface RS side of the window CW-a. The flat portion FA may be parallelto a plane defined by the first direction DR1 and the second directionDR2. Each of the bent portions BA may be a curved surface portion whichis adjacent to the flat portion FA and each of the bent portions BA mayhave a curved shape. For example, referring to FIG. 3 , the bentportions BA may be portions which are adjacent to opposite sides of theflat portion FA and are bent downward from the flat portion FA. However,the present inventive concept is not limited thereto, and the bentportion BA may be disposed adjacent to only one side of the flat portionFA, or the bent portions BA may be disposed adjacent to all four sidesof the flat portion FA when viewed in a plane.

FIG. 4 is a cross-sectional view illustrating the window according to anembodiment of the present inventive concept. FIG. 4 is a cross-sectionalview taken along line I-I′ in the window CW illustrated in FIG. 2 .Hereinafter, a description of the cross section of the window CW will begiven. This window may be the same as the window illustrated in FIG. 2 ,but the description may also be applied to the window CW-a of theembodiment illustrated in FIG. 3 .

Referring to FIG. 4 , the window CW includes the front surface FS and arear surface RS, which are each external surfaces. The front surface FSof the window CW is externally exposed and defines the front surface ofthe electronic device EA. The rear surface RS of the window CW isopposed to the front surface FS in the third direction DIG.

The window CW may include one or more compressive stress regions CSL.Each of the compressive stress regions CSL may be formed adjacent to asurface of the window CW. The compressive stress region CSL may beformed to have a predetermined depth in a thickness direction of thewindow CW from the surface of the window CW. In this specification, thecompressive stress region CSL may indicate a region from the frontsurface FS or the rear surface RS, which is the surface of the windowCW, to a point where compressive stress becomes zero. Referring to FIG.4 , the window CW may include two compressive stress regions CSL whichare respectively disposed adjacent to the front surface FS and the rearsurface RS, and are formed to be symmetrical with respect to a centerline MP of the window CW. However, the present invention is not limitedthereto, and the compressive stress region CSL may be provided adjacentto only the front surface FS of the window CW, or the compressive stressregions CSL adjacent to the front surface FS and the rear surface RS maybe provided asymmetrically with respect to the center line MP of thewindow CW.

In the window CW of an embodiment of the present inventive concept, abase region BSL may be provided between the compressive stress regionsCSL. The base region BSL may be a region where ion exchange by atoughening molten salt does not occur during the toughening of the baseglass in manufacturing the window.

The compressive stress region CSL may include Li⁺, Na⁺, and K⁺ ions. Thecompressive stress region CSL may include a first compressive stressportion CSP1 adjacent to the front surface FS or the rear surface RS,which is “the surface,” and a second compressive stress portion CSP2adjacent to the base region BSL. The second compressive stress portionCSP2 may be a portion disposed adjacent to the first compressive stressportion CSP1.

FIG. 5A shows distributions of Li⁺, Na⁺, and K⁺ ion concentrations forthe window CW according to an embodiment of the present inventiveconcept. In FIG. 5A, the abscissa represents depth from depth of zero,which is the surface of the window CW, toward the center line MP, andthe ordinate represents relative ion concentration.

Referring to FIG. 5A, the first compressive stress portion CSP1 may be aportion in which, from the surfaces FS and RS toward the base regionBSL, the concentration of the K⁺ ion decreases and the concentration ofthe Na⁺ ion and the concentration of the Li⁺ ion increase. In the secondcompressive stress portion CSP2, the concentration of the Na⁺ ion maydecrease and the concentration of the Li⁺ ion may increase, in adirection toward the base region BSL.

In the window CW, the first compressive stress portion CSP1 may includeeach of the Li⁺, Na⁺, and K⁺ ions, and the second compressive stressportion CSP2 may include the Li⁺ and Na⁺ ions but might not include theK⁺ ion. On the other band, the concentration of the Li⁺ ion and theconcentration of the Na⁺ ion in the base region BSL may be maintained ata constant level.

The first compressive stress portion CSP1 may correspond to acompressive stress region formed through second toughening step (S530;see FIG. 8 ) and third toughening step (S550; see FIG. 8 ) in the methodof manufacturing a window according to an embodiment of the presentinventive concept. Also, the second compressive stress portion CSP2 maycorrespond to a compressive stress region formed in first tougheningstep (S510; see FIG. 8 ).

A thickness t_(DOC) of the compressive stress region CSL from thesurface (the front surface or the rear surface) may be at least about10% of a total thickness t_(CW) of the window CW. The thickness t_(DOC)of the compressive stress region CSL is a thickness in a depth directionof the window CW from the front surface FS or the rear surface RS of thewindow CW to a point where a compressive stress value becomes zero.

In addition, a thickness t_(DOL-K) of the first compressive stressportion CSP1 may represent a thickness from the front surface FS or therear surface RS of the window CW to a point where the concentration ofthe K⁺ ion becomes zero. For example, the first compressive stressportion CSP1 may be a layer formed by K⁺ ion exchange.

The thickness t_(DOC) of the compressive stress region CSL may be withina range from about 130 μm to about 150 μm. Further, the thicknesst_(DOL-K) of the first compressive stress portion CSP1 may be within arange from about 5 μm to about 15 μm. The window CW may have improvedimpact resistance by including a compressive stress region CSL having athickness that is at least about 10% of the total thickness t_(CW).

The thickness t_(CW) of the window CW may be within a range from about0.3 mm to about 1.0 mm. For example, the thickness t_(CW) of the windowCW of an embodiment of the present inventive concept may be within arange from about 0.7 mm to about 0.9 mm. The window CW may be used as acover window of the electronic device EA (see FIG. 1 ) described indetail to make the electronic device EA (see FIG. 1 ) slimmer andlighter, by having a small thickness ranging from about 0.3 mm to about1.0 mm.

The window CW may be provided by chemically toughening a base glassincluding SiO₂, Al₂O₃, and Li₂O₃. Thus, the base region BSL may includethe SiO₂, Al₂O₃, and Li₂O₃. The base region BSL may include SiO₂ of fromabout 50 wt % to about 80 wt %, Al₂O₃ of from about 10 wt % to about 30wt %, and Li₂O₃ of from about 3 wt % to about 20 wt %.

FIG. 5A shows the ion concentration distributions of the alkali ions(the Li⁺, Na⁺, and K⁺ ions) from one surface to the center line MP, butthe ion concentration distributions of the alkali ions (the Li⁺, Na⁺,and K⁺ ions) from the other surface to the center line MP may also beshown likewise.

In the window CW of an embodiment, density may be highest in the firstcompressive stress portion CSP1 and may become lower toward the centerline MP. Density in the second compressive stress portion CSP2 may belower than density in the first compressive stress portion CSP1, andhigher than density in the base region BSL.

FIG. 5B exemplarily shows a compressive stress profile in the window CWof an embodiment of the present inventive concept. FIG. 5B may be agraph showing a compressive stress profile of a window CW manufacturedby the method of manufacturing a window to be described later. In FIG.5B, the arrow direction representing compressive stress corresponds to adirection in which the compressive stress increases. The compressivestress profile from one surface to the center line MP is shown in FIG.5B, but a compressive stress profile from the other surface to thecenter line MP may also be shown similarly.

Referring to FIG. 5B, the window CW of an embodiment may have a highestcompressive stress value on the front surface FS and the rear surfaceRS, and have a gradually decreasing compressive stress value toward thecenter line MP of the window CW. A compressive stress value may benegative beyond the thickness t_(DOC) of the compressive stress regionCSL. A negative compressive stress value may represent a tensile force.

The compressive stress profile in the compressive stress region CSL mayhave at least one inflection point CS_T. In FIG. 5B, the inflectionpoint CS_T may appear at a portion corresponding to a boundary betweenthe first compressive stress portion CSP1 and the second compressivestress portion CSP2. The window CW may exhibit a compressive stressprofile including at least one inflection point CS_T.

In the window CW of an embodiment of the present inventive concept, thefirst compressive stress portion CSP1 may have a first compressivestress pattern PT1 having a first slope, and the second compressivestress portion CSP2 may have a second compressive stress pattern PT2having a second slope. The slopes of the compressive stress profile inthe first compressive stress portion CSP1 and the second compressivestress portion CSP2 each correspond to an amount of decrease incompressive stress value as a depth inside the window CW increases fromthe surface of the window CW toward the base region BSL.

The first slope of the first compressive stress pattern PT1 in the firstcompressive stress portion CSP1 may be a ratio of an amount ΔCS1 ofdecrease in compressive stress value to an amount Δt1 of depth increaseinside the window CW. In addition, the second slope of the secondcompressive stress pattern PT2 in the second compressive stress portionCSP2 may be a ratio of an amount ΔCS2 of decrease in compressive stressvalue to an amount Δt2 of depth increase inside the window.

Δt1 is an amount of depth increase from the surface to a depth of thethickness t_(DOL-K) of the first compressive stress portion CSP1, andΔCS1 corresponds to a difference between a compressive stress valueK′_CS at the surface and a compressive stress value K′_CS1 at theinflection point CS_T. Here, Δt2 is an amount of depth increase from thedepth of the thickness t_(DOL-K) of the first compressive stress portionCSP1 to an end of the second compressive stress portion CSP2 opposed tothe inflection point CS_T, and ΔCS2 corresponds to the compressivestress value K′_CS1 at the inflection point CS_T.

Referring to FIG. 5B, an amount of change in compressive stress value inthe first compressive stress portion CSP1 may be greater than an amountof change in compressive stress value in the second compressive stressportion CSP2. For example, the first slope may be greater than thesecond slope. The inflection point CS_T occurring in the compressivestress profile may be a point at which the first slope of the firstcompressive stress pattern PT1 is changed to the second slope of thesecond compressive stress pattern PT2.

A compressive stress value at the surface of the window CW may begreater than or equal to about 650 MPa. By having a maximum surfacecompressive stress value of about 650 MPa or greater, the window CW mayhave excellent impact resistance.

FIGS. 6A to 6C each show, by way of example, an embodiment of acompressive stress profile in the window. Each of compressive stressprofiles shown in FIGS. 6A to 6C may include three pattern portionswhile the compressive stress profile shown in FIG. 5B has the twocompressive stress patterns.

First pattern portions PT1_a, PT1_b, and PT1_c correspond to thecompressive stress profile in the second compressive stress portion CSP2(see FIG. 4 ). Second pattern portions PT2_a, PT2_b, and PT2_c and thirdpattern portions PT3_a, PT3_b, and PT3_c correspond to the compressivestress profile in the first compressive stress portion CSP1 (see FIG. 4). The third pattern portions PT3_a, PT3_b, and PT3_c respectivelycorrespond to compressive stress profiles from the surface of the windowto inflection points in the first compressive stress portion CSP1 (seeFIG. 4 ). The second pattern portions PT2_a, PT2_b, and PT2_crespectively correspond to compressive stress profiles of portionsdisposed between the first pattern portions PT1_a, PT1_b, and PT1_c andthe third pattern portions PT3_a, PT3_b, and PT3_c. For example, thesecond pattern portions PT2_a, PT2_b, and PT2_c respectively correspondto profiles of change of compressive stress from compressive stressvalue K_CS included in the first compressive stress portion CSP1 (seeFIG. 4 ) to the compressive stress value K′_CS1 at the depth of thethickness t_(DOL-K).

The compressive stress profiles shown in FIGS. 6A to 6C may representcompressive stress for the window manufactured by the method ofmanufacturing a window of an embodiment to be described later. Forexample, the compressive stress profiles shown in FIGS. 6A to 6C may beobtained from performing a three-stage toughening process that proceedssequentially. For example, the first pattern portions PT1_a, PT1_b, andPT1_c may be compressive stress profiles formed from the firsttoughening, and the second pattern portions PT2_a, PT2_b, and PT2_c andthe third pattern portions PT3_a, PT3_b, and PT3_c may correspond to thecompressive stress profiles formed by performing the second and thirdtoughening, respectively.

In FIGS. 6A to 6C, K′_CS is the final compressive stress value at thesurface, and K_CS is the compressive stress value at the inflectionpoints where the second pattern portions PT2_a, PT2_b, and PT2_c arerespectively changed to the third pattern portions PT3_a, PT3_b, andPT3_c, and K′_CS1 corresponds to the compressive stress value at theinflection points where the first pattern portions PT1_a, PT1_b, andPT1_c are respectively changed to the second pattern portions PT2_a,PT2_b, and PT2_c.

FIGS. 6A to 6C show the compressive stress profiles having the shapes,different from each other, of the third pattern portions PT3_a, PT3_b,and PT3_c. The window CW may have a compressive stress value increasingtoward the surface in the third pattern portion PT3_a, as shown in FIG.6A.

In addition, referring to FIGS. 6B and 6C, compressive stress values inthe third pattern portions PT3_b and PT3_c may decrease toward thesurface. FIG. 6B shows a case in which the difference is not largebetween the final compressive stress value K′_CS at the surface and thecompressive stress value K_CS at the inflection point where the secondpattern portion PT2_b is changed to the third pattern portion PT3_b. Incontrast, FIG. 6C shows a case in which the final compressive stressvalue K′_CS at the surface is significantly smaller than the compressivestress value K_CS at the inflection point where the second patternportion PT2_c is changed to the third pattern portion PT3_c.

Accordingly, the window may exhibit a compressive stress profile havingthe largest compressive stress value at the surface as shown in FIG. 5Bor FIG. 6A, or may have a compressive stress profile having a slightlysmaller compressive stress value at the surface as shown in FIG. 6B orFIG. 6C.

The window may have excellent surface strength by including the firstcompressive stress portion which is adjacent to the surface and has arelatively large slope, which is defined as the amount of decrease incompressive stress value as a depth inside the window increases from thesurface toward the center of the window. The second compressive stressportion has a smaller slope of compressive stress value relative to thefirst compressive stress portion. Further, the window may include, inthe compressive stress region, the first compressive stress portion inwhich, from the surface toward the center, the concentration of the K⁺ion decreases, the concentration of the Na⁺ ion and the concentration ofthe Li⁺ ion increase, and the second compressive stress portion inwhich, toward the center, the concentration of the Na⁺ ion decreases andthe concentration of the Li⁺ ion increases, thereby having excellentimpact resistance with a large surface compressive stress value.

Hereinafter, the method of manufacturing a window, according to anembodiment of the present inventive concept, will be described withreference to FIGS. 7 to 9 . In the description of the method ofmanufacturing a window in accordance with an embodiment of the presentinventive concept, a description of certain elements has been omitted toprovide a simplified disclosure. It should be assumed that thoseelements that are not described may be at least similar to correspondingelement that are described elsewhere in the disclosure.

FIG. 7 is a flowchart illustrating the method of manufacturing a windowin accordance with an embodiment of the present inventive concept. Themethod of manufacturing a window may include providing a base glass(S100) and toughening the base glass (S500). In addition, the method ofmanufacturing a window may further include polishing the base glass(S300) after having provided the base glass (S100).

In the method of manufacturing a window according to an embodiment ofthe present inventive concept, the base glass having been provided(S100) may be a base glass manufactured by a float process. Also, theprovided base glass may be manufactured by a down draw process or afusion process. However, the present invention is not limited thereto,and the provided base glass may be manufactured by various methods notspecified herein.

The base glass having been provided (S100) may be cut and providedbefore the toughening of the base glass (S500) in consideration of theuse purpose. For example, the cut base glass may be provided before thepolishing of the base glass (S300), and a side surface, the frontsurface, or the like of the cut base glass may be polished. However, thepresent invention is not limited thereto, and the provided base glassmay be of a size not matching that of a final product to which theprovided base glass is applied, and then may be cut and processed tomatch the size of the final product after a process of manufacturing awindow therefrom.

The base glass may be flat. Alternatively, the base glass may be bent.For example, the base glass that is cut and provided in consideration ofthe size of the final product may be convexly or concavely bent withrespect to a middle portion thereof. Alternatively, the base glass mayinclude a bent portion in an outer portion thereof. However, the presentinvention is not limited thereto, and the base glass may be provided invarious different shapes.

The base glass so provided (S100) may include SiO₂, Al₂O₃, and Li₂O₃.For example, the base glass may include SiO₂ of from about 50 wt % toabout 80 wt %, Al₂O₃ of from about 10 wt % to about 30 wt %, and Li₂O₃of from about 3 wt % to about 20 wt %.

In an embodiment of the present inventive concept, the base glass mayinclude SiO₂, Al₂O₃, Li₂O₃, and Na₂O. The base glass may further includeP₂O₅, K₂O, MgO, and/or CaO in addition to SiO₂, Al₂O₃, Li₂O₃, and Na₂O.

The polishing of the base glass (S300) may be performed after theproviding of the base glass (S100). The side surface of the base glass,which is a cut surface of the base glass that is cut in various ways,may be polished using an abrasive or the like. Further, the frontsurface of the provided base glass may be processed using an abrasive orthe like.

The toughening of the base glass (S500) may be a chemically tougheningof the base glass that is performed by providing a toughening moltensalt to the base glass. For example, the toughening of the base glass(S500) may toughen the surface of the base glass by an ion exchangemethod after immersing the base glass in the toughening molten salt. Thetoughening molten salt provided to the base glass may include two ormore kinds of alkali ions.

The toughening of the base glass (S500) may be achieved by exchangingalkali metal ions having a relatively small ionic radius on the surfaceof the base glass for alkali metal ions having a larger ionic radius.For example, the toughening of the surface may be achieved by exchangingLi⁺ ions and Na⁺ ions on the surface of the base glass for Na⁺ ions andK⁺ ions provided in the toughening molten salt, respectively. The windowCW manufactured through the toughening of the base glass (S500) mayinclude the compressive stress region CSL (see FIG. 4 ) on a surfacethereof. The compressive stress region CSL (see FIG. 4 ) may be formedon the front surface FS and/or the rear surface RS of the window CW.

In the method of manufacturing a window according to an embodiment ofthe present inventive concept, the toughening of the base glass (S500)may include three-stage toughening. FIG. 8 is a flowchart illustratingthe toughening of the base glass (S500) in the method of manufacturing awindow in accordance with an embodiment of the present inventiveconcept. The toughening of the base glass (S500) may include firsttoughening in a first toughening molten salt (S510), second tougheningin a second toughening molten salt (S530), and third toughening in athird toughening molten salt (S550). The first to third toughening steps(S510, S530, and S550) in the method of manufacturing a window of anembodiment may be sequentially performed. The first to third tougheningsteps (S510, S530, and S550) may be performed through separateprocesses, respectively.

Each of the first to third toughening molten salts provided in the firstto third toughening steps (S510, S530, and S550) may be a molten saltincluding two or more kinds of ions from among Li⁺, Na⁺, K⁺, Rb⁺, andCs⁺. For example, each of the toughening molten salts provided in thefirst to third toughening steps (S510, S530, and S550) may include amolten salt of KNO₃ and NaNO₃ as a mixed salt.

The weight percentages of KNO₃ and NaNO₃ in the toughening molten saltsprovided in the first to third toughening steps (S510, S530, and S550)may vary stage by stage. For example, the weight percentages of KNO₃ andNaNO₃ included in the second toughening molten salt used in the secondtoughening steps (S530) may respectively be different from the weightpercentages of KNO₃ and NaNO₃ included in the first toughening moltensalt used in the first toughening steps (S510). In addition, the weightpercentages of KNO₃ and NaNO₃ included in the second toughening moltensalt used in the second toughening steps (S530) may respectively bedifferent from the weight percentages of KNO₃ and NaNO₃ included in thethird toughening molten salt used in the third toughening steps (S550).The weight percentage of KNO₃ in the second toughening molten salt maybe greater than the weight percentage of KNO₃ in the first tougheningmolten salt or the third toughening molten salt.

For example, the weight ratio of KNO₃ and NaNO₃ in the second tougheningmolten salt may be within a range from about 91:9 to about 90:10. Forexample, the second toughening molten salt may include a relativelylarger amount of KNO₃ among KNO₃ and NaNO₃.

The first toughening molten salt used in the first toughening steps(S510) of the method of manufacturing a window may include KNO₃ andNaNO₃ in a weight ratio of 50:50. By comparison, the second tougheningmolten salt used in the second toughening steps (S530) may include KNO₃and NaNO₃ in a weight ratio of 92:8. In addition, the third tougheningmolten salt used in the third toughening steps (S550) may include KNO₃and NaNO₃ in a weight ratio of 50:50.

Also, in a method of manufacturing a window in accordance withembodiments of the present inventive concept, the third toughening steps(S550) may be performed for a shorter time than the first tougheningstep (S510) or the second toughening step (S530). For example, while thefirst toughening step (S510) and the second toughening step (S530) eachlast from about 120 minutes to about 240 minutes, the third tougheningstep (S550) may be performed from about 10 minutes to about 60 minutes.

In the method of manufacturing a window, the toughening of the baseglass (S500) may be performed at a temperature of about 350° C. to about450° C. For example, the toughening of the base glass (S500) may beperformed at a temperature of about 380° C. to about 400° C. A processtemperature of the second toughening step (S530) may be lower than aprocess temperature of the first toughening step (S510) or the thirdtoughening step (S550).

The toughening molten salt in the first toughening may further includean additive. For example, the first toughening molten salt may furtherinclude H₂O₃Si or zeolite in addition to KNO₃ and NaNO₃.

FIG. 9 schematically illustrates the toughening of the base glass(S500), which provides the toughening molten salt to toughen the baseglass, in the method of manufacturing a window. FIG. 9 exemplarilyillustrates a toughening processing unit HU in which the toughening step(S500) is performed. The toughening processing unit HU in FIG. 9 isschematically illustrated for describing the toughening step (S500), andthe configuration of the toughening processing unit HU is not limited tothat illustrated in FIG. 9 .

The toughening processing unit HU illustrated in FIG. 9 may include atank HT for containing a toughening molten salt ML in molten form. Aheating unit HP is disposed so as to at least partially surround thetank HT. The heating unit HP heats the toughening molten salt ML in thetank HT. A drive unit HD fixes a provided base glass BG and moves thebase glass BG in a vertical direction so as to immerse the base glass BGin the toughening molten salt ML. A control unit HC controls theoperation of the toughening processing unit HU. The control unit HC maycontrol the temperature of the toughening molten salt ML contained inthe tank HT. For example, the control unit HC may control the heatingunit HP so that the toughening molten salt ML is heated to apredetermined temperature and a temperature of the toughening moltensalt ML is maintained at the temperature to which the toughening moltensalt ML has been heated. For example, the heating unit HP may provideheat so as to heat the toughening molten salt ML, or may function as aninsulating unit for maintaining the temperature of the heated tougheningmolten salt ML. The base glass BG may be disposed so as to be entiretyimmersed in the toughening molten salt ML.

Only two base glasses BG which are fixed to the drive unit HD andtreated in the toughening molten salt ML are illustrated exemplarily inFIG. 9 , but the inventive concept is not limited thereto. The baseglass BG which is treated in the toughening molten salt ML may besingularly provided or may be provided in plurality.

Referring to FIG. 9 , the toughening step (S500) may be performed in thetoughening processing unit HU by immersing the base glass BG in thetoughening molten salt ML. In the method of manufacturing a window inaccordance with embodiments of the present inventive concept, the firstto third toughening steps (S510, S530, and S550) may be performed inseparate toughening processing units HU, respectively. However, thepresent invention is not limited thereto, and toughening stages usingthe same toughening molten salt may be performed in the same tougheningprocessing unit HU.

Tables 1 and 2 below respectively show process conditions of the methodsof manufacturing a window according to a Comparative Example and anExample of the present disclosure, and evaluation results of propertiesof the windows of the Comparative Example and the Example manufacturedtherefrom.

The same base glass is toughened for the Comparative Example and for theExample, the evaluation result of the window toughened through atwo-stage toughening process is shown for the Comparative Example, andthe evaluation result of the window toughened through a three-stagetoughening process is shown for the Example.

The toughening in the method of manufacturing a window has beenperformed under the conditions shown in Table 1 below.

TABLE 1 Comparative Classification Condition Example Example FirstTemperature (° C.) 395 395 Toughening Time (min) 240 240 Ratio of Salts(K:Na) 50:50 50:50 Second Temperature (° C.) 380 380 Toughening Time(min) 150 150 Ratio of Salts (K:Na) 92:08 92:08 Third Temperature (° C.)395 — Toughening Time (min)  15 Ratio of Salts (K:Na) 50:50

Table 2 shows the evaluation results of the windows manufactured underthe conditions of the Example and the Comparative Example.

TABLE 2 Compressive t_(DOC-K) t_(DOC) Breakage Threshold ClassificationStress (MPa) (μm) (μm) Height (cm) Example 699.7 6.2 133.0 60.5Comparative 681.6 5.8 138.7 56.0 Example

A breakage threshold height shown in Table 2 is defined as a method ofevaluating the surface strength of the window, and is a measured heightat which the window is broken when a weight having a predeterminedweight is dropped onto a ball after the ball is placed on the window tobe evaluated. For example, it may be seen that as the breakage thresholdheight increases, the window has higher impact strength.

Referring to the results of Table 2, the window of the embodiment hassimilar compressive stress value and depth of the compressive stressregion as compared with those of the window of the comparative example,but shows an improved breakage threshold height.

Accordingly, the method of manufacturing a window according to anembodiment of the present inventive concept may include an additionalthird toughening to allow the window to have, in the compressive stressregion, the ion concentration distribution and the compressive stressprofile different from those of the window of the comparative example,so that the window of an embodiment may have improved impact resistanceeven when the compressive stress value or the compressive stress regionat the surface are similar to those of the window of the comparativeexample.

The window in accordance with an embodiment of the present inventiveconcept may have increased impact resistance by having a highcompressive stress value at the surface and by including the firstcompressive stress portion and the second compressive stress portionhaving ion concentration distributions different from each other. Inaddition, in the method of manufacturing a window, the window may have ahigh surface compressive stress value and excellent impact resistance byincluding the three-stage toughening and by increasing the percentage ofa salt having K⁺ ions in the second toughening step.

In an embodiment of the present inventive concept, the window havingimproved surface strength characteristics may be provided by includingthe compressive stress portions having different concentration profilesof the alkali ions.

In an embodiment of the present inventive concept, the method ofmanufacturing a window having excellent impact strength may be providedby including the toughening step which has three or more stages.

Although embodiments of the present inventive concept have beendescribed herein, it is understood that various changes andmodifications can be made by those skilled in the art within the spiritand scope of the inventive concept.

What is claimed is:
 1. A window comprising: a base region; and acompressive stress region disposed on the base region and including Li⁺,Na⁺, and K⁺ ions, wherein the compressive stress region comprises: afirst compressive stress portion in which a concentration of the K⁺ ionsdecreases, a concentration of the Na⁺ ions increases, and aconcentration of the Li⁺ ions increases, from a surface of the windowtoward the base region; and a second compressive stress portion adjacentthe first compressive stress portion, wherein, in the second compressivestress portion, the concentration of the Na⁺ ions decreases and theconcentration of the Li⁺ ions increases from the first compressivestress portion toward the base region.
 2. The window of claim 1,wherein: the first compressive stress portion has a first compressivestress pattern in which a compressive stress value decreases with afirst slope from the surface toward the base region, the secondcompressive stress portion has a second compressive stress pattern inwhich the compressive stress value decreases with a second slopedifferent from the first slope, from the first compressive stressportion toward the base region, and each of the first slope and thesecond slope is defined as an amount of decrease in the compressivestress value as a depth inside the window increases in a direction fromthe surface toward the base region.
 3. The window of claim 2, whereinthe first slope is greater than the second slope.
 4. The window of claim1, wherein a density of the first compressive stress portion is greaterthan a density of the second compressive stress portion.
 5. The windowof claim 1, wherein the second compressive stress portion does notcomprise K⁺ ions.
 6. The window of claim 1, wherein the thickness of thecompressive stress region is within a range from about 130 μm to about150 μm.
 7. The window of claim 1, wherein the thickness of the firstcompressive stress portion is within a range from about 5 μm to about 15μm.
 8. The window of claim 1, wherein a compressive stress value at thesurface is about 650 MPa or larger.
 9. The window of claim 1, whereinthe base region comprises SiO₂ of from about 50 wt % to about 80 wt %,Al₂O₃ of from about 10 wt % to about 30 wt %, and Li₂O₃ of from about 3wt % to about 20 wt %.
 10. The window of claim 1, wherein the windowcomprises a flat portion and at least one bent portion adjacent to theflat portion.
 11. A window comprising a compressive stress region at asurface thereof, wherein the compressive stress region comprises; afirst compressive stress portion in which a concentration of the K⁺ ionsdecreases, a concentration of the Na⁺ ions increases, and aconcentration of the Li⁺ ions increases, from the surface toward acenter of the window; and a second compressive stress portion adjacentto the first compressive stress portion, wherein, in the secondcompressive stress portion, the concentration of the Na⁺ ions decreasesand the concentration of the Li⁺ ions increases from the firstcompressive stress portion toward the center.
 12. The window of claim11, wherein: the first compressive stress portion has a firstcompressive stress pattern in which a compressive stress value decreaseswith a first slope from the surface toward the center, the secondcompressive stress portion has a second compressive stress pattern inwhich the compressive stress value decreases with a second slope greaterthan the first slope, from the first compressive stress portion towardthe center, and each of the first slope and the second slope is anamount of decrease in the compressive stress value as a depth inside thewindow increases from the surface toward the center.
 13. The window ofclaim 1, wherein the second compressive stress portion is adjacent tothe first compressive stress portion and wherein the second compressivestress portion is disposed between the first compressive stress portionand the base region.
 14. The window of claim 11, wherein the secondcompressive stress portion is adjacent to the first compressive stressportion and wherein the second compressive stress portion is disposedbetween the first compressive stress portion and the center of thewindow.